1. Field of the Invention
This invention pertains to spinal implants and surgical procedures for use in spinal stabilization. More particularly, this invention pertains to an apparatus and method for implanting a tapered implant between two vertebrae.
2. Description of the Prior Art
Chronic back problems can cause pain and disability for a large segment of the population. In many cases, the chronic back problems are attributed to relative movement between vertebrae in the spine.
Orthopedic surgery includes procedures to stabilize vertebrae. Common stabilization techniques include fusing the vertebrae together. Fusion techniques include removing disk material which separates the vertebrae and impacting bone into the disk area. The impacted bone fuses with the bone material in the vertebrae to thereby fuse the two vertebrae together.
To increase the probability of a successful fusion, spinal implants have been developed. Commonly assigned U.S. Pat. No. 5,489,307 discloses a hollow threaded cylindrical implant. That patent also discloses a method of placing the implant between two vertebrae.
The method of U.S. Pat. No. 5,489,307 discloses parallel distraction of opposing vertebrae prior to placing an implant. However, not all vertebrae are in parallel opposition. A normal and healthy spine has a natural curvature referred to as lordosis. As a result of the curvature, opposing vertebrae are positioned with their end plates in non-parallel alignment depending upon the position in the spine. For example, in the lumbar region of the spine, the end plates of the L-4 and L-5 vertebrae may be at an angle of about 3xc2x0-15xc2x0. Similarly, the opposing end plates of the L-5 and S-1 vertebrae may be at about 8xc2x0-16xc2x0 lordosis. The actual amount of lordosis varies with the location of the spine and varies from patient to patient. It is desirable to provide an implant which maintains or achieves a desired lordosis between opposing vertebrae and a method of placing the implant.
According to one embodiment of the present innovation, a spinal implant is disclosed having a taper from a leading end to a trailing end equal to a desired lordosis.
In an alternative embodiment, a spinal implant can have two tapers. According to this embodiment the implant has a first taper diverging away from the axis of the implant from the leading end to a terminal end. A second taper diverges away from the axis of the implant from the terminal end to the leading end. The tapers meet at the xe2x80x9ctrailing end risexe2x80x9d. The xe2x80x9ctrailing end risexe2x80x9d (TRE) and the terminal end are collectively referred to as the trailing end. In a preferred embodiment the implant has a terminal end and a leading end which are of substantially equal diameters.
The method of the invention includes placing a tapered distraction plug into the disk space between the vertebrae on one side of the vertebrae. On the opposite side of the vertebrae, a tapered tap is used to tap a thread pattern into the opposing vertebrae. The implant is placed into the tapped space.